Novel fault isolation scheme under protection failure in MVDC distribution networks without DC circuit breakers

In medium voltage direct current (MVDC) distribution networks without DC circuit breakers, converters with fault-blocking capability are employed to de-energize the network, which facilitates the disconnection of DC switches. The fault current is cleared rapidly under DC faults, posing difficulties to the reliable fault isolation due to the rapid disappearing fault features. To tackle this problem, a novel isolation scheme based on active control of converters is proposed, where trapezoidal wave current is injected from the converter to the fault point. The faulty line could be located by counting the number of high-level pulses of trapezoidal wave current, and then isolated by the corresponding DC switches during the low-level pulses of trapezoidal wave current. Finally, the healthy parts of the network could be restored to normal operation. Compared with other fault location & isolation methods, the proposed scheme based on the active control of converters could cooperate with DC switches without communication. In addition, the innovative utilization of the number of injected pulses rather than the amplitude or frequency can provide a backup function if the DC switch fails to operate. The proposed scheme further improves the reliability of the MVDC network and is easy to apply, the effectiveness of the proposed scheme is verified in PSCAD/EMTDC.